The Maine Homeowner's Guide to Radon

Why Maine Has Some of the Highest Radon in the Country

Maine isn't just unlucky — it's geology. The same granite bedrock that makes Maine beautiful is what creates one of the worst radon problems in the United States.

Radon is a naturally-occurring radioactive gas produced by the decay of uranium in soil and rock. Maine sits on a vast bed of uranium-rich granite, and that bedrock continuously generates radon as it decays. The gas moves upward through soil pores, fractures in the bedrock, and into homes through basement cracks, sump pits, and even through well water.

Here's what makes Maine different from the rest of the country:

• EPA Zone 1 coverage: Almost every county we serve — Kennebec, Cumberland, Androscoggin, Penobscot, York, Sagadahoc, Lincoln, Oxford — is classified Zone 1 (the highest-risk category, predicted indoor levels above 4 pCi/L). Only some coastal areas in Knox and Hancock counties drop to Zone 2.
• Maine averages roughly 30% of homes above 4 pCi/L — the EPA's national action level. The U.S. average is about 6%. Some Maine towns regularly see median levels above 4 pCi/L, meaning more homes need mitigation than don't.
• Well water radon is uniquely a Maine problem. Maine has one of the highest rates of private well usage in the country (~50% of households), and Maine wells routinely test in the tens of thousands of pCi/L for waterborne radon — among the highest readings in the U.S.
• Tight, well-insulated Maine homes trap radon better than older drafty construction. Energy-efficient homes built in the last 30 years often test higher than older farmhouses, not lower.

None of this is meant to scare you. It's meant to put context behind a single number on a test report. If you live in Maine and your home tests above 4 pCi/L, you're not unusual — you're typical.

What Radon Actually Does to Your Health

Radon is the second-leading cause of lung cancer in the United States after smoking — and the leading cause among non-smokers. The EPA estimates 21,000 Americans die from radon-induced lung cancer each year.

Here's what's actually happening: radon gas itself is mostly inert when inhaled, but as it decays, it produces radioactive "daughter products" (polonium-218, polonium-214) that attach to dust particles. When you breathe those particles in, they lodge in your lung tissue and emit alpha radiation directly into the cells lining your airways. Over years and decades, this damages DNA and can cause cancer.

The risk is cumulative and dose-dependent — meaning longer exposure at higher levels means higher risk. There's no "safe" level (the EPA notes that even outdoor air contains ~0.4 pCi/L), but the action level of 4 pCi/L is where the cost-benefit math clearly favors mitigation. The World Health Organization recommends action at the lower 2.7 pCi/L threshold.

Children, in particular, get a higher dose per inhaled particle because their lungs are still developing and they breathe more rapidly relative to body size. If you have kids and your home tests above 4 pCi/L, the risk math gets stronger.

How to Test Your Home (and What the Numbers Mean)

Testing is fast, inexpensive, and the only way to know your real radon level. We don't sell testing services — we focus exclusively on mitigation — so you can trust this section is genuine advice, not a sales pitch.

Three testing options:

1. Charcoal canister (short-term). $15–$30 from any hardware store, lab fee usually included. Sits in your basement for 2–7 days under closed-house conditions. Mail it in. Get results in about 2 weeks. Best for screening.
2. Alpha-track detector (long-term). $30–$50. Sits for 90 days to a year. Gives you a true average exposure rather than a snapshot. Best for confirming a borderline short-term result.
3. Continuous radon monitor (CRM). $150–$300 for a quality consumer device (Airthings, Corentium). Sits permanently in your home, displays current and average levels, and shows you how levels fluctuate with weather, season, and HVAC. Best for ongoing peace of mind.

Closed-house conditions matter

For any short-term test, windows and doors must be closed (except for normal entry/exit) for 12 hours before and during the test. Without this, you're not measuring what regulators care about. Don't run a test during severe weather (radon levels can spike or drop unrepresentatively).

What the numbers mean

For a faster ranking against the dose curve, see our Radon Risk Calculator or the "What radon level is dangerous?" explainer.

Mitigation: How It Works and What It Really Costs

The good news: radon mitigation is one of the most reliable home repairs you can make. A properly designed system reduces radon by 80–99%, lasts 10+ years on a single fan replacement, and costs less than most people fear.

The dominant technique: Sub-Slab Depressurization (SSD)

For 95% of Maine homes, the answer is the same: a 3" or 4" PVC pipe is connected through the basement slab to the gravel/soil beneath. A continuously-running inline fan (typically 25–90 watts) creates negative pressure under the slab and draws radon out before it can enter living space, exhausting it above the roofline. Done right, the system is nearly silent indoors and disappears into the architecture.

For crawlspaces, the same principle is applied beneath a heavy-duty sealed vapor barrier. For homes with mixed foundations (basement + crawlspace), we typically install one fan that handles both via a manifold.

Real Maine pricing (2026)

For an instant estimate tailored to your home, use our Cost Calculator.

Operating cost is small: a typical fan uses about $5–$12 per month in electricity and lasts 10–15 years before replacement (~$300 with labor).

Radon in Well Water — Maine's Hidden Problem

If you have a private well in Maine, you have a second radon problem that air mitigation doesn't solve. About 1 in 5 Maine wells tests above the proposed EPA limit of 4,000 pCi/L for waterborne radon, and many test in the tens of thousands.

Waterborne radon becomes airborne when the water is agitated — showers, dishwashers, washing machines, faucets. The general rule of thumb: every 10,000 pCi/L in water adds roughly 1 pCi/L to indoor air. So a well at 30,000 pCi/L is contributing about 3 pCi/L of airborne radon — enough to push an otherwise-fine home above the action level.

Activated carbon filters are not adequate for high-radon wells. They concentrate radioactive material in the filter and can become a hazard themselves. The professional solution is an aeration system installed at the well point, which strips radon from water and vents it outside before water enters the home.

If you're testing your home, we strongly recommend testing both air and water if you're on a private well. Many homeowners discover their well water is the dominant radon source.

Radon and Real Estate Transactions

In Maine, radon shows up in nearly every residential transaction. Maine's mandatory Property Disclosure Statement asks specifically about radon testing and mitigation. Here's how to handle it from each side of the table.

If you're selling

Get tested before listing. If results are above 4 pCi/L, mitigate before going to market. A pre-existing professional system documented in your disclosures is worth far more than a credit at closing — buyers see it as a positive. A failed buyer's test mid-contract often results in larger price concessions than the actual mitigation cost.

If you're buying

Always include a radon contingency in your offer. If a test comes back high, the standard remedy is for the seller to install a professional mitigation system before closing — not a credit. A credit leaves you with the work to manage post-move.

If you're an agent

Have a list of NRPP-certified mitigators ready, with realistic pricing. Mitigation almost always solves the deal — what kills deals is uncertainty and missed deadlines. We routinely complete pre-closing installations within one week. See our Real Estate Transaction page for documentation samples and timelines.

Your 30-Day Action Plan

If you're starting from zero, here's the path:

1. Days 1–3. Order a charcoal canister test ($15–$30 at any Maine hardware store) or a continuous radon monitor (longer-term, $150–$300). If you're on a well, also order a water radon test through your county Cooperative Extension or Maine HETL.
2. Days 4–10. Run the test under closed-house conditions. Keep windows shut (other than normal entry/exit) for 12 hours before and through the test period.
3. Days 11–18. Mail in or read your results. If above 4 pCi/L, request mitigation quotes — most reputable Maine mitigators will give a flat-rate quote either over the phone or after a brief site visit.
4. Days 19–25. Schedule installation. Most installations take a single day with the homeowner present. Plan for some noise (drilling) for 30–60 minutes.
5. Days 26–30. Run a post-mitigation test 24 hours to 30 days after installation to confirm levels have dropped. A reputable mitigator will retest at no additional charge if the first install doesn't bring levels below 4 pCi/L.

That's it. Three to four weeks from "I should probably test" to "my home is safe and documented." For comparison, the average Maine homeowner waits years between learning about radon and acting on it.

Frequently Asked Questions